In this project we are coupling standard techniques of genetics, epidemiology, infectious disease and immunology in the study of disorders which may be due to disordered immunity. Such disease include multiple sclerosis. This approach is expected to clarify the etiology of these disease, indicate individuals or populations at high risk and suggest mechanisms for prevention and treatment. Laboratory study of carefully selected patients includes serologic study of antibody titer to various infectious agents, genetic make-up of the major histocompatibility complex and the humoral ahd cellular pattern of immune response. BIBLIOGRAPHIC REFERENCE: Horton, W., Eldridge, R., Brody, J.: Familial Motor Neuron Disease: Evidence for at Least Three Different Types. Neurology 26:460-465, May 1976.